HLA class II-restricted CD4+ T cells play a critical role in cellular immunity and are a key component of anti-tumor immune responses. CD4+ T cells provide necessary help to tumor-specific CTLs (Topalian 1994. Curr Opin Immunol 6:741-745) and produce cytokines such as interferon gamma (IFNγ), which can activate antigen presenting cells and mediate other immunological effects (Corthay et al., 2005. Immunity 22:371-383). Experimental results in several systems have demonstrated that CD4+ T cells are necessary for an effective anti-tumor immune response. Given the importance of CD4+ T cells in generating a robust immune response, an optimally designed cancer immunotherapy or anti-tumor vaccine should induce both tumor-specific CD4+ and CD8+ T cells for maximal efficacy.
The design of cancer immunotherapies and vaccines has benefited greatly from the identification of tumor-associated antigens. One such antigen, HER-2/Neu, is a prime target for such strategies due to its amplification in a variety of cancers, including breast and ovarian cancer. The HER-2/Neu oncogene encodes a transmembrane glycoprotein with homology to epidermal growth factor receptor (Coussens et al., 1985. Science 230:1132-1139). Overexpression of HER-2/Neu occurs in approximately 30% percent of breast adenocarcinomas and is associated with aggressive disease and a poor prognosis. As a result, several immunological approaches designed to increase T cell recognition of the HER-2/Neu protein have been tested in clinical trials. Characterizing the resulting HER-2/Neu-specific T cell responses in such studies has led to the identification of several HLA class I and class II-restricted T cell epitopes within the HER-2/Neu protein (Sotiriadou et al., 2001. Br J Cancer 85:1527-1534). The identification of these epitopes has, in turn, enhanced our ability to detect and quantitate HER-2/Neu-specific T cell response. Such information leads to improved designs for effective immunotherapies and provides a better understanding of the role of HER-2/Neu-specific T cell in eradicating HER-2/Neu-expressing tumors.
The usefulness of a defined T cell epitope is limited by its HLA-restriction. Peptide epitopes typically form productive peptide-MHC complexes with a small number of HLA alleles and stimulate T cell responses only in individuals expressing those alleles. This confines immunological studies and clinical trials to individuals of a specific HLA type, often 20% or less of the general population. So-called promiscuous T cell epitopes, which can be presented by a larger number of HLA alleles, have been described for several tumor antigens. Promiscuous T cell epitopes can bind to multiple HLA alleles to stimulate antigen-specific T cells, allowing for the induction and study of T cell responses in individuals of different HLA types. Additionally, promiscuous epitopes are valuable because the immunotherapies and vaccines based on these epitopes can be widely applicable to the general population for cancer treatment and prevention. Thus, there exists a clear need for new information relating to previously unknown promiscuous epitopes of tumor antigens.
The present inventors have identified a series of novel promiscuous T cell epitopes in the HER-2/Neu protein sequence. These epitopes, located within the region of 270-284 or 268-286 of the HER-2/Neu protein, are recognized by a CD4+ T cell clone generated from a patient treated with an autologous, active cellular immunotherapy for HER-2/Neu overexpressing carcinomas (Valone et al., 2001. Cancer J 7 Suppl 2:S53-61). The T cell clone recognizes these peptide epitopes presented in the context of at least 25 different HLA-DRB1* alleles. Antibody blocking experiments confirm that the recognition is HLA-DR restricted. Furthermore, these epitopes are naturally processed and presented from exogenous protein antigen. The promiscuity of these epitopes for different HLA-DRB1* alleles makes these epitopes a valuable tool for evaluating HER-2/Neu-specific immune responses regardless of HLA type. Additionally, these epitopes can be used as a universal CD4 T helper cell epitope in peptide-based vaccines or immunotherapies for the treatment HER-2/Neu+ cancers.